Space discharge device



May 22, 19 45. R. E. MCCOY SPACE DISCHARGE DEVICE Filed April 5 1941 3Sheets-Sheet 1 ROBERT E. M CDY INVENTOR.

BY ATTORNEY.

May 22, 1945. R C 2,376,797 v SPACE DISCHARGE DEVICE Filed April 5, 19415 Sheets-Sheet 2 FUBEIQT E. MCEY INVENTOR.

BY 6 Z ATTORNEY.

y 1945- R. E. M coY 2,376,707

SPACE DISCHARGE DEVICE Filed April 5, 1941 s Sheets-Sheet s FDfiEET E. MCUY INVENTOR.

' 2. 0 5 ATTORNEY.

/.0 fig:

X TBHNS/T TIME 0 DE'FL EC T/O/V FREOUENC Y Patented May 22, 1945 UNITEDSTATES PATENT OFFICE 2,376,707 SPACE. DISCHARGE DEVICE. Robert E. McCoy,Portland, mg. Application April 5, 1941, Serial No. 387,029

14 Claims.

This invention relates to improvements in space-discharge devices; andmore particularly, it relates to those in which the charged particlesare caused to travel a considerable distance.

The principal object of my invention is to provide convenient andefficient means for the conversion of power from direct current toalternating current, or vice versa, which will function at very highfrequencies. The invention is capable of even wider utility since itprovides means for converting power from one frequency to another, orfor the exchange of power among circuits operating with severaldifferent frequencies of alternating current and circuits operating withdirect current. Moreover, it provides means whereby a small amount ofpower at one frequency can control a larger amount of power at the samefrequency or another frequency related thereto; or a small amount ofalternating current power can control a large amount of direct currentpower, or vice versa.

Since my invention depends largely upon the dynamic properties of an ionbeam, it has a secondary object; namely, to improve the sensitivity andefficiency of the means whereby the motion of such a beam is controlled.

These and other objects will appear as my invention is more fullyhereinafter described in the following specification illustrated in theaccompanying drawings and finally pointed out in the appended claims.

In the drawings:

Figure 1 is a longitudinal, sectional elevation of a cathode-ray tube.

' Figure 2 is a sectional, detail view of an electron gun taken on theline 2-2 of Figure 1.

Figure 3 is a perspective view of an electron gun.

Figure 4 is a graph showing the variation of deflection sensitivity, andcomparing the deflection produced by the two systems mentioned.

Figure 5 shows a number of patterns typical of those which would betraced on the screen of an oscilloscope whose deflection system had beenreplaced by that illustrated in Figure 1, if only one pair of deflectionplates was energized.

Figure 6 is a graph showing the variation of the deflection sensitivity,as indicated by the major and minor axes of the elliptic patternsillustrated in Figure 5.

ings:

The preferred embodiment of my invention is shown in Figure 1. Itscomponent parts are located in or near a cylindrical'glass tube 1 form-Referring now more particularly to the drawmg a discharge chamber. Thewhole consists of five overlapping zones, generally indicated as A, B,C, D, and E, whose functions are as follows:

Within the zone A, I provide an electron gun, generally indicated at 2,whose function is to discharge electrons throughout the length of thedischarge chamber. Within the zone B, I provide means, generallyindicated at 3, for deflect ing the electrons coming from the electrongun within the zone A. Within the zone C, I provide a deflection boostergenerally indicated at 4. Zone D is practically empty; but around theoutside of the tube, I provide a simple armature -5. At the end of thetube in zone E, I provide a plurality of electrodes, generally indicatedat 6, for collecting the electrons at the end of their passage throughthe discharge chamber. v

I shall now explain the operation of the device as a whole, treatingeach zone as a unit; then I shall describe the operation of each zone indetail. For the general explanation, fice to describe the resultsobtained by the elements of each zone, leaving the discussion of themeans until later.

The electron gun 2 in zone A produces a beam of electrons which itshoots or projects along the axis of the tube into the zone B.

For convenience, the subsequent movements of the beam will be describedby locating a typical electron in a system of polar co-ordinates. Theco-ordinates used will be: the axial distanoe, measured from somearbitrary point, such as the end of zone B; the radial distance,measured from the beam to the nearest point on the axis; and the angleof the azimuth, which indicates the direction of the radial line in aplane perpendicular to the axis.

In zone B, transverse forces, alternating at a high frequency, deflectthe beam. When the beam passes from zoneB to zone C, it has a smallradial displacement. Successive electrons differ slightly in azimuth,since the deflection system is designed to make the azimuth rotate insynchronism with the alternation'of the deflecting forces.

In zone C, the radial displacement of the beam is increased. For thisreason, zone C may be called a displacement magnifier, or a deflectionbooster. It makes possible the use of relatively small forces in thedeflection zone B.

The beam leaves zone C, and travels through zone D at a substantiallyconstant distance from the axisand close to the glass, along a path suchas those indicated by the dotted lines.

Due to the rotation of the azimuth of the beam,

it will sufit is close to each armature conductor in turn. At onemoment, it may be close to one conductor; a half-cycle (at deflectionfrequency) later, it will be close to an opposite conductor. Byelectromagnetic induction, the periodic changes in beam positiongenerate alternating voltages in the armature conductors.

By the same process of electromagnetic induction, alternating currentsin the armature conductors induce alternating electric fields within thetube. The beam, by its changes in position, commutates the alternatingfields into the equivalent of a D. C. voltage in series with the beam.

Thus a transfer of power takes place from beam to armature circuits, orvice versa.

The beam then proceeds into zone E, where the electrons are collected byone of the electrodes, and conducted through the external D. C. circuitsback to their starting point.

The electrical characteristics of my invention are very much like thoseof a more familiar device known variously as a synchronous converter, arotary converter, or a double current generator.

To make the analogy complete, the mechanical type converter should bedeprived of the usual stationary field magnet; it should have separateA. C. and D. C- windings on the armature; and the relative motion ofcommutator and brushes should be produced by a small two-polesynchronous motor.

In the mechanical verter:

Direct current flows from In the cathode-ray con verter:

Direct current flows from an external circuit, through one brush andcommutator segment, then through the I) C. armature coils, to anothercommutator segment and brush; thence it returns to the external circuit.

The relative motion of brushes and commutator an external circuit,causing electrons to move from the cathode, through the defied tion zoneB, then through zone D, to the anode in zone E; thence the electronsreturn to the external circuit.

The changing azimuth of the deflection changes the path of the electronsthrough zone D. There are bars changes the path of the D. C. through thearmature coils. There may be several dozen difierent commutator bars,and a corresponding number of paths through the D. C. armature.

The frequency with which the D. C. returns to the same path is the sameas the frequency of A. C. in the small motor.

In either case, the direct current produces a magnetic field which, byits rotation relative to the A. C. armature conductors, generatesalternating voltages therein.

Alternating currents in the A. C. armature coils of the mechanicaldevice induce alternating voltages in the adjacent D. C. armature coils.The relative motion of brushes and commutator converts these inducedvoltages into a direct voltage, so far as the external D. C. circuit isconcerned.

Alternating currents in the armature conductors of the electronic deviceinduce alternating voltage gradients in the space adjacent. Theelectrons moving through zone D integrate these induced gradients into adirect voltage, which is effectively in series with the beam, so far asthe external D. C. circuit is concerned.

Power may be transferred in either direction from beam (D. C.) toarmature (A. C.) or from armature to beamdepending on the phase rela-'tionships in the A. C. circuits.

If the .electron gun in zone A were of conventional design, such asthose used in cathode-ray oscilloscopes or in television picture tubes,the possible power output would be small (because of the small beamcurrent).

trillions of electrons in motion at one time, and a cor respondingnumber of diiferent paths through zone D.

The frequency with which any path is repeated is the same as thefrequency supplied to the deflector sys tem.

Because it provides a beam of higher current with no largercross-section, I prefer to use the gun structure illustrated in zone A,Figure 1, and shown in more detail in Figures 2 and 3.

With reference to the electron gun, the emitting surface of the cathode1 is shown horizontal in Figures 2 and 3. Flanking it on either side areauxiliary electrodes 8 and 9. Above the cathode (and therefore not shownin Figure 1) is an accelerating anode I0. All four of these electrodes1, 8, 9, and ID, are situated between the poles II and [2 of magnet l3.

A second anode I 4, containing a long, narrow aperture I5, is placedperpendicular to the emitting surface 1, near the ends of electrodes 9and ID.

A third accelerating anode l6 faces the second.

Perpendicular to most of the electrodes already mentioned is a fourthanode I! which contains a small aperture l8.

Facing the edges of electrodes [4, l 6', and l I are the poles of asecond magnet l9, oriented substantially at right angles to thedirection of the first magnet l3.

With reference to Figure 1, the apparatus shown in Figures 2 and 3 islocated within the tube I with the flat surface of electrode l1perpendicular to the axis. The aperture I8 in electrode 11 is centeredon the axis.

Forwardly of the fourth anode H, but still in zone A, is a focusinganode 20. This consists of a hollow conducting cylinder, containing twoapertured discs, 2! and 22. The apertures are situated on the axis ofthe tube, which is also the axis of the cylindrical portion of thefocusing anode.

Emitting surface 7 and auxiilary electrodes 8 and 9 are at the samepotential. Anode I0 is at much higher potential.

The electrostatic field, due to this potential difference, tends toaccelerate electrons upward. In addition, because of the shape andinclination chosen for the auxiliary electrodes 8 and 9, the electricfield tends to draw toward the middle these electrons which are near theright or left edge of the cathode I. This side-thrust is relativelysmall, but it plays an important part in compressing the electronstream.

The first magnet I3 produces a magnetic field which is parallel to thesurfaces of electrodes 1, 8, and 9, but perpendicular to theelectrostatic field.

Electrons emitted by the cathode 1 are accelerated upward by theelectric field; but as soon as they start to move, the magnetic fielddeflects their paths sidewise. The resultant paths are shown in Figure 2for electrons starting near the edges of the cathode, and for anelectron starting near the middle.

The important characteristic to be noted is the convergence of thevarious paths, as they approach the second anode 14. The thickness ofthe electron stream, as it passes through aperture 15, is very much lessthan the widthof the emitting surface 1. The improvement in theconcentration of the beam depends upon the shape of electrodes 8, 9, andID, the position of aperture l5 relative to the cathode 1, and the ratioof the electric field intensity. This ratio can be controlled readily byadjusting the potentials of the electrodes.

Upon emerging from the aperture I 5, the beam will be in the form of athin horizontal stream, which is still wide in the direction normal tothe paper in Fig. 2. Electrodes 14, I6, and I1, together force in itsownin single file, when 11th the second magnet is, compress the beam inhis direction, and rotate it in a manner which :orresponds. closely tothat employed by electrodes Hi, and i together with the first magnetP31.

As a result of the two-stage compressionof the seam, it emerges from thefar side of aperture H3 in the form of a slender stream. Its crosssection is still approximately the same shape as the surface of thecathode, but the cross-sectional area is perhaps a hundred-fold smaller.

Theoretically, if, the electrons left the cathode with no initialvelocities, and if they did not repet one another because of theirelectrical charge. the cross section of the beam could be compressed toamillionth part of the cathode area, merely by refining the design ofthe system just described. However, because of the complicationsmentioned, there is a limit tothe improvement possible by precision inthe design and. construction.

In. practice, the beam will emerge aperture N3 of electrode II with thevarious elec tron velocities directed almost along the tube axis, but.there will be a trace of radial velocity.

The focusing electrode is typical of the electron lens systems commonlyemployed in cathode-ray tubes. As the beam of electrons. passes throughit, the electrostatic field (determined. by the shape and. potential ofthe electrode surfaces near the beam) changes the radial velocities ofthe electrons, causing them to approach the axis instead of divergingfrom it. The result is similar to the effect of a. convex lensv on abeam of light.

To some extent, the beam may be focused by adjusting the potentials ofelectrodes l4 and H (the second and fourth anodes, respectively).. Ifthis adjustment proves sufficient, electrode 21] may be omitted.

For reasons that, will become evident later on. it is desirable that thefocal length of the electron lens should be relatively long; in fact,the cross-over, where the electrons start to. diverge againaftercrossing the axis, should be located a near the middle of zone D.

The basic principle employed to compress the beam in zone A isequallyzapplicable to space discharges of other types. The relativeintensities of the electric and magnetic fields required dependon theratio of charge to mass for the particles in the discharge. ciple of thebeam compression is:

Charged particles enter the gion with velocities in the same generaldirection as the electric field which they encounter. Besides theelectric field. the region contains a magnetic field which issubstantially perpendicular to these initial velocities. At first. theforces on the moving particles due to the two fields are perpendicular,since an electric field exerts a direction, while a magnetic field actsat right angles to both its own direction and that of the movingparticles. As the particles turn from their initial direction, themagnetic force turn too, so that it tends more and more to oppose theforce of the electric field. In the end, the particles leave thecompressor region with very little velocity in their initial direction,and with a much higher component of velocity perpendicular to thatdirection. Particleswhich enter the region side by side leave itsubstantially the direction which was at first sidewise becomes theprincipal direction of movement, and therefore forward.

This effect will reduce the transverse extent of the beam, as measuredin the plane of the electric and magnetic forces acting on it, but will'from the compressor re-.

To be precise, the prinnot directly affect its extent in the directionof the magnetic field. If the beam is thin enough in that direction,well and good; if not, a second compressor region, suitably orientated,can reduce. the extent of the beam in the other direction.

The same result may be achieved regardless of the source of thedischarge or the distance traversed by the particles before they enterthe compress'or region, although the structure used to provide thenecessary fields may differ in detail from that shown in Figure 2- and.Figure 3, [16- I pending on the extent to which it can be combirred withadjacent structures.

Within the tube l-,. in zone: B, is a set of defiection plates, such asthose used in the more common types of cathode ray tubes. Figure 1 showsone pair of plates, 23 and 2 perpendicular to the plane of the drawings,and one plate 25 of another pair parallel to the plane of the paper.

Outside the tube l, a little distance beyond the ends: of the deflectionplates are two annular pole pieces, 26 and 21', concentric with thetube. Joining the outer peripheries of 26 and 21 are a number ofmagnetized bars, such as 28 and 29. Between the bars and the glass tube1 are magnet coils, 30 and 3| co-axial with the tube.

Direct currents passing through the coils 3i! and 31, together with theresidual magnetism of the bars 28 and Z9 and. the pole pieces 26 and 21,produce a magnetic field within the tube. In the vicinity of thedeflection plates 23, 24, and 25 and its companion plate, this field isuniform and parallel to the axis.

Alternating voltages are supplied to each pair of deflection plate froma-suitable source, such as an oscillator disposed outside the tube l.The frequency used is very high-from megacycles to several billioncycles per second.

The phase relation betweenthe alternating voltages is so adjusted thatthe resultant electric field between the plate is substantiallyequivalent to a uniform electrostatic field revolving in synchronismwith the alternating voltages.

Due to this revolving electric field, the electrons in zone B experiencetransverse forces. Like the field, the force exerted on each electron isuniform; but it changes in azimuth as the field rotates.

Under its influence, the electron gradually acquires a transversecomponent of. velocity in addition to it original velocity parallel tothe axis.

The axial magnetic field does not affect the axial velocity, but itdoes. exert a transverse force upon the electron at right angles to thetransverse velocity. This tends to rotate the direction of thetransverse velocity at the gyromagnetic frequency, which is proportionalto the magnetic flux. density (about. 2-8. megacycles per gauss). Ingeneral, the relation between magnetic field intensity and gyromagneticfrequency may be expressed as or B 2.1rfm/q path as it passes betweenthe deflection plates 23, 24, and 25. When it passes beyond theinfluence of the deflecting forces, it will continue along a tangent ofthe spiral. Successive electrons will leave zone B at difierentazimuths, depending on theazimuth of the electric field.

The conventional system oikdefiection (without the axial magnetic fieldof critical intensity) would act in a somewhat similar manner, exceptthat the spiral would return to the axi at intervals if allowed tocontinue. Due to this elfect, the deflection sensitivity of theconventional system is seriously reduced at high frequencies. In fact,at some frequencies, the conventional system will not produce anydeflection.

Figure 4 is a graph showing the variation of deflection sensitivity, andcomparing the deflection produced by the two systems mentioned.

' The abscissae of the graphs represent the product of the deflectionfrequency by the transit time; where the deflection frequency is definedby the alternating transverse force acting upon the electrons, whilethey are in the deflection zone B; and the transit time is defined asthe time required for an electron of the beam to pass from one end ofthe deflection zone to the other. Since For example, if the transit timeis one-billionth of a second, then abscissa, 1.0 represents a frequencyof 1,000 megacycles per second, abscissa 2.0 represents a frequency of2,000 megaoycles per second, and so on.

The ordinates of flection sensitivity; flection produced at the graphsrepresent the dethat is, the ratio of the dethe frequency in question tothat which would be produced at a very low frequency, if the samevoltage were applied to the deflection plates in each case.

The upper curve 32 in Figure 4 shows the deflection sensitivity of mysystem (with critical axial magnetic field). The lower curve 33 inFigure 4 shows the deflection sensitivity of the conventional system(without the axial field).

The mathematical process required to calculate the deflectionsensitivity is rather involved, and will not be stated here. However,the advantage of my system is obvious from Figure 4.

There is still another the axial magnetic field specified. It permitsthe The deflection can be described most readily in terms of the patternwhich the beam would trace on a plane perpendicular to the axis.

When both pairs of deflection plates are in action,

32 or as at 33, in Figure 4,

When only one pair of plates is active, with the assistance of criticalaxial magnetic field, the pattern will be elliptical. Typical patternsfor this case are shown in Figure 5. Each of these patterns is drawnwith its center at the abscissa indicating the frequency. For some ofthe patterns, the abscissae of their centers have been indicated bylight vertical lines, which are continuations of the corresponding linesin Figures 4 and 6. I

The two curves in Figure 6 show the maximum and minimum radius of theelliptical pattern;

that is, they show the deflection sensitivity. Ti. scale of Figure 6 isthe same as that of Figure Note that the average radius is just half ofthe obtained with both pairs of deflection plate working, and that thedifierence between maxi mum and minimum radii is small at high frequencies.

There are three possible arrangements for zonl B: The conventionalsystem (with no axial mag. netic field) could be used; but then it wouldbe necessary to increase the magnification of zone C, to compensate forthe low sensitivity; and the velocity of the beam might have to beadjusted to avoid the condition of zero deflection sensitivity.

A second possibility is the use of a conventional deflection systemcapable of producing a circular deflection pattern by itself, and theuse of critical axial magnetic field in addition. This is illusone formof electrostatic diiflculty in the operation of the cathode-rayconverter. Furthermore, it is much easier to adjust a D. C." magneticfield than it is to adjust two A. C. circuits at frequencies such as 200or .300 megacycles. The saving in cost, due to eliminatpair ofdeflection plates attendant A. C, circuits, will offset most of the costof the magnet structure.

In zone C, the tube contains three electrodes which may be describedgenerally as cup-shaped. The first one 35 is comparatively flat-morelike a saucer than a cup; it has a small aperture 36 3! has a much lowerpotential, not much higher than the cathode. Electrode 39 has a higherpotential than 31, and perhaps higher than electrode 35the exact valuedepends on the velocity desired for the electrons in zone D.

' in the axial component of velocity,

35 in electrode 35, they have scarcely left the axis. On this account,only a small aperture is needed to let them pass. Between electrodes 35and 31, the axial velocity of the electrons drops gradually, unitl itreaches a minimum as the electrons pass through the aperture 38 inelectrode 31. The minimum may be very low, even smaller than the radia1component of velocity, if the potential or electrode 31 is made lowenough.

While the axial velocity is retarded in the first part of zone C, theradial velocity suffers little change. The radial motion continues, andmay carry the electrons halfway to the glass of tube l by the time theyreach the aperture 38. For this reason, the aperture in electrode 31must be fairly large to allow the beam to pass through.

Between the aperture .38 in electrode 31 and the end of electrode 39,the electric field gradually restores the axial velocity. While thischange is taking place, the electrons continue their radial motion,until they almost reach the glass.

If the shape of the electrodes is properly selected, their potentialscan be adjusted to make the electric field between electrodes 3'! and 39reduce the radial velocity just before the electrons pass from zone 'Cto zone 1). In any case, the axial velocity will be many times theradial velocity as the electrons leave zone C.

It is not .actually necessary to use three electrodes in zone C. Thefirst electrode 35 serves mainly as an electrostatic shield between zoneB and zone D. In addition, it serves to keep electrode 31 from reducingthe axial velocity of the electrons in zone B. However, it could beeliminated at the cost of some added diificulty in adjusting thepotentials of the other electrodes on either side of it.

Electrode 39 could also be dispensed with, under some circumstances. Itsmain function is to restore the axial velocity of the electrons, to themagnitude desired in zone D, while they are still close to electrode 31.If the space available between electrode 31 and zone B were sufficient,electrode 39 could be omitted. Then the electrons would regain theiraxial velocity due to the influence of an electrode in zone E which hasa higher potential than would be chosen for electrode 39. The boundaryof zone C would be rather indefinite-somewhere between electrode 3-! andzone ill-and zone C might overlap considerably into zone D.

If the beam consisted of positively charged particles, instead ofelectrons, the various electrodes would require potentials of polarityopposite to those mentioned above, but otherwise similarly related. Thesame principle applies to zone C in any case: reduce the axial velocityof the particles temporarily, to give the transverse component ofVelocity time to produce the desired displacement within a, limitedaxial distance, then restore the velocity to a magnitude more suitablefor subsequent use of the beam.

Zone C may be considered as a compound electron lens. From thisviewpoint, the electrostatic field from electrode 35 to electrode 31 isequivalent to a concave lens, while the field from electrode 3-! toelectrode 39 is equivalent to a convex lens. The first lens causes thebeam to diverge more steeply from the axis, while the second lens has anopposite effect.

In general, if the path of the beam leaving the deflection zone B wereprojected backward, it would intersect the axis at a point near themiddie of the deflection zone. This point of interarc of a helix,outside section would be substantially the same regardless of the degreeof deflection. For convenience, it will be called hereinafter thedeflection center. If, in a similar manner, a straight line were drawnbackward along the direction of the beam as it left the first lens, thisline would intersect the axis at a point farther from zone B, which maybe called the first image point, because it is the location at which thefirst lens produces a virtual image of the deflection center. This pointtoo is substantially independent of the degree of deflection.

The two electron lenses are so placed that the first focal point of thesecond lens coincides with the first image point of the first lens; thusthe beam is directed parallel to the axis as it leaves the second lensin accord with the general rule that any ray passing through the focalpoint of a lens will emerge parallel to the axis.

In this application, the lens action aifects the beam as a whole,instead of the individual electrons within the beam, and it does notbring the electrons to a focus at the end of the tube as a conventionallens system would do. electrodes 35, 31, and 39 must be considerablylarger and farther apart than the electrodesof any lens system designedto focus the beam in the usual sense of the word, by overcoming thedivergent tendencies of the individual electrons.

In zone D is an armature, much "simpler in structure than most of thosein common use, but the same in principle. It consists of a number ofconductors-perhaps a score at most-such as iii and 41. Each of them isdisposed along an the discharge chamber. Some of these conductors areconnected to others at their extremities; and some are connected to A.C. circuits more or less remote from the armature, just as in the caseof more commonly used armatures. In Figure l, the armature has ten mainconductors, which are connected in pairs at the left and right endsalternately. One pair,

4t and M, are connected to the external load circuit, not shown; this isindicated by the horizontal extension of conductor 4|, which extendsbeyond the right end of the discharge chamber l; the correspondingextension of conductor 40 would be above the plane of the paper, andtherefore does not appear in the drawings.

Within the tube l, zone D is almost empty. Its boundaries are somewhatuncertain, but may be considered to be close to electrode 39 of zone C,and close to electrode 42 in zone E This latter electrode is a disc,perpendicular to the axis of the tube.

Individual electrons in zone D travel substantially parallel to the axisof the discharge chamber l. Successive electrons difier slightly inazimuth, due to the design of the deflection system. As a result, theelectrons in various parts of zone D at any instant are disposed alongan arc of a helix. As time goes on, the electrons advance, and the helixrotates (one revolution for each cycle of deflection in zone B) Thepitch of the helix may be computed from the speed of the electrons andthe deflection frequency, since the two motions are related in the samemaner as the linear motion of a nut and the rotation of a screw whichdrives it.

The helical form of the armature conductors is chosen to match that ofthe electron stream, so that the conductors closest to the beam at anygiven moment will be substantially parallel to it.

Strictly speaking, the situation is not quite so Physically,

simple as the foregoing description, but is scarcely possible to explainthe precise form most suitable for the armature conductors withoutmathematics. Allowance should be made for the action of the armature asa group of transmission lines; for the effect of the currents in the endconnections of the armature; and for the propagation time of theelectro-magnetic field. Under some circumstances, it may be advisable touse different degrees of skew in alternate conductors of the armature,or a special curve near the ends of the conductors.

As viewed from the armature, the electron stream within the tube isindistinguishable from a current of electricity flowing in a helicalconductor which revolves at high speed. Since the beam current isconstant, it produces a magnetic field which is likewise constant, andwhich revolves with the current. The revolving magnetic flux cuts thestationary armature conductors, inducing alternating voltage in them.The fundamental frequency of the generated voltage, like the rotationalspeed of the beam, is the same as the deflection frequency used in zoneB. However, the wave-form is nonsinusoidal; it may be analyzed quencieswhich are harmonics of the fundamental, including the fundamentalfrequency itself.

By a suitable choice of the sequence of the interconnections between thefrequency devices. In practice, therefore, only the desired frequency isof much importance.

For example, with the ten armature conductors shownin Figure 1,connected together alternately at left and right ends, to. form a simpleten-pole wave-wound armature, the output voltage will harmonic of thedeflection freq'uency,-the th harmonic, the th, etc. Assuming a beamcurrent of 0.1 ampere, deflection freat 1500 megacycles per second, plus2.59 volt at 4,500 megacycles per second, 0.434 volt at 7,500 megacyclesper second, and smaller voltage comcurrent depends on two factors: thesize of the .into sinusoidal components having fre-.

ode.

beam, which is proportional to the electrode dimensions; and the currentdensity, which de pends on the shape of the electrodes and the currentdensity at the emitting surface of the cath- According to Myers (page496, Electron Optics, D. Van Nostrand Company, Inc., New York, 1939) themaximum current density attained in the prior art was 3.2 to 6.4 amperesper square centimeter. Assuming a current density of '5 amp/sq. cm., itmay be calculated that a 0.100 ampere beam would require a diameter of1.6 millimeters or approximately 1% inch. With an improved type ofbeam-forming device, such as that shown here (see Figures 2 and 3), muchhigher current densities might be obtained; and at 10 or 20 amperes persquare centimeter, the maximum beam current might be over an ampere.

From the law of conservation of energy, when the armature delivers A. C,energy to an external circuit, a like amount of energy must be takenfrom the beam; and when the armature receives A. C. energy from anexternal source, a like amount of energy must be gained by the electronsin the beam. If no other influence acted on the electrons in zone D, thearmature currents would retard or accelerate them, depending on whetherthe armature delivers or receives A. C. energy at its terminals.

For example, if electrodes 39 and 42 were both at a potential 5000 voltsabove the cathode, the electrons would enter zone D with a. velocity ofabout 4,200,000,000 centimeters per second. If then the armaturecurrents acted to retard the beam by the equivalent of 1000 volts, theelectrons would leave zone D with a velocity corresponding to that whichonly 4000 volts would produceabout 3,750,000,000 centimeters per second;and if the effect of the armature was reversed (by reversing thecurrents), would leave zone D at a velocity (about 4,700,000,000centimeters per second) corresponding to a total voltage of 6000. Inthese two cases, the electrons would approach electrode 42 at velocitieswhich would be expected if the armature had no effect but the potentialof electrode 42 differed by 1000 volts from its actual potential.

In practice, it is desirable that the electrons travel at asubstantially uniform velocity in zone D. The potential of electrode 42is therefore adjusted to a value which makes the electrostatic armaturecurrents. In the example above, when the armature currents retard theelectrons, electrode 42 must be raised to a potential of 6000 volts tokeep the electrons moving evenly; and when the armature currents act toaccelerate the electrons, electrode 42 must be lowered to a potential of4000 volts, instead of the 5000 originally asstuned.

The information thus derived is sufificient for the operation of myinvention, but not for the design problems. Consider the eflect ofarmature currents in more detail.

the armature and the hypothetical conductor. Given the armature current,

. in each of the imaginary conductors which may be supposed to occupysuccessive short segments of its path.

In making this summation, take the voltage of each segment as of themoment the electron passes it, regardless of the voltage in that segmentbefore or afterward. The limit of the total as the number of imaginarysegments is indefinitely increased will be the true voltage induced forthe electron by the armature currents. The effect of this voltage mustbe combined with the eifect of the D. C. electrostatic field in zone Dto determine the net result.

Because the voltages induced in the imaginary conductors arealternating, that does not mean thatthe voltage affecting the electronis alternating; the electron moves from one place to another at highspeed, so that it can (if the circumstances are favorably adjusted)enter a section of zone D while the induced voltage is momentarily "inone direction, and leave that section before the direction of thevoltage reverses; and since successive sections of zone D may very wellhave induced voltages of opposite polarity, the next section that itenters may just at that moment be reversing its polarity to become asthe first section was a moment earlier. By its motion relative to thealternating field, the electron commutates the induced voltage.

'If the armature currents all vary similarly, as in a single phasesystem, the induced voltages in various parts of zone D may be ofopposite polarities, but they will all increase and decreasesimultaneously. Their effect on the electrons will not be evenlydistributed along the path of'the electron, and therefore cannot beentirely neutralized by the D. C. electrostatic field at every point.Consequently, the speed of the electrons will vary somewhat as they passthrough zone D; however, the average velocity can be kept the same astheinitial velocity, by adjustment of the D. C. electrostatic field.

If the armature currents form a balanced polyphase system, the inducedvoltages will not differ greatly in amplitude, for points equallydistant from the axis, and the phase angle of these voltages will varygradually with changes in azimuth or axial position. As a result, itwill be possible for electrons to pass through zone D without muchchange in velocity; the effect of the induced Voltages on the electronwill be so nearly uniformly distributed that the D. C. electrostaticfield can compensate almost perfectly for their influence on the speed.

In zone E, there are several electrodes. Electrode 42 is a circulardisc, concentric with the tube l, and perpendicular to the axis of thetube. Electrode 43 is a circular cylinder, co-axial with the dischargechamber 1. One end of it is near the edge of electrode 42, so that anarrow annular aperture is formed by the gap. The other end is closer tothe end of the discharge chamber, and farther from zone D. Electrode 44is roughly conical in shape, with the wide end toward zone D; it lieswithin electrode 43, but not in contact with that electrode. Electrode45 is shaped more or less like a horn; it is symmetrical about the axisof the discharge chamber, like all the other electrodes in zone E; itencloses part of the lead 46 which connects electrode 42 to the externalcircuits; and it closes most of the opening in the small end ofelectrode 44.

In operation, electrode 42 is adjusted to a potential suiiicient tomaintain substantially constant velocity among the electrons in zon D.

Electrode 43 is at a potential which does notd-ifl'er greatly from thatof 42. Electrodes 4'4 and 45 are at considerably lower potentials, whichare adjusted in accord with the voltage induced for the electrons by thearmature currents in zone D.

There are two modes of operation. In cases when the electrode voltagesneed not be adjusted very often, electrode 44 is maintained at apotential above the cathode which is slightly higher than the voltageinduced along the beam in zone D. As a result, the electrons passingbetween electrodes 42 and 43 are retarded by the electrostatic fieldbetween those electrodes and electrode 44; they strike it (44) with onlya low velocity, corresponding to the slight excess of potential by whichelectrode 44 overcomes the retarding effect of the induced voltage towhich the electrons were subjected in zone D. Electrode 45 is at apotential a little lower than that of electrode 44, and serves to repelany electrons emitted from the surface of that electrode, and to drivethem back so that they will not reach electrode 42.

The other mode of operation, preferred when the conditions changerapidly, so that manual adjustment of the electrode potentials isdiflicult or impossible, is as follows:

Electrodes 42 and 43 are maintained at high potentials, as before.Electrode 44 is maintained at a potential considerably higher than isnecessary merely to allow the electrons to reach it. The electronsstrike it with such force that additional electrons are emitted from itssurface. These secondary electrons are attracted to electrode 45, whichis at a potential slightly higher than electrode 44.

If the potential of electrode 44 is excessively high, the number ofsecondary electrons will be great, and a large current will flow betweenelectrodes 44 and 45. If the potential drops too low, the number ofsecondary electrons will decline, reducing the current of electrode 45.This variation of current can be used to operate devices which willadjust the electrode potentials to more nearly the proper value. Thecontrol devices which could be used range elaborate systems of relaysand motor driven switches for changing the D. C. supply voltage.

For many cases, electrode 43 may be connected to electrode 42 at anypoint where it is convenient to do so, and the connection does notobstruct the path of the beam. In other cases, it may prove convenientto keep electrode 43 at a potential slightly lower than electrode 42, inorder to deflect the electrons slightly toward the axis as they passthrough the aperture between 42 and 43. In still other cases, electrode43 may be omitted entirely, on the grounds that it does not add enoughto the control of the electron paths to justify its cost of manufacture.Then the diameter of electrode 44 would have to be increased.

It is highly probable that experienc will indicate some modifications ofthe shapes of electrodes 44 and 45, to make them more effective andlimit the number of electrons which stray from their intendeddestination.

When the cathode-ray converter is used as an amplifier, the operatingprocedure will be about as follows: First, test the D. C. supplycircuits, and adjust the electrode potentials to appropriate values.Then start the oscillator which controls the deflection, and adjust itto the desired frequency.

After the deflection system is set in operation, adjust the potentialsof the electrodes in the defrom simple imped ances in the externalcircuits of the electrodes to flection booster, zone C, to make the beampass between electrodes 42 and 43 in zone E without striking either.For'this stage of the procedure, electrodes 44 and 45 need not be morethan 50 or 100 volt above the cathode potential; electrodes 42 and 43should be at about the same potential as electrode 39. The adjustmentwill be easier if the face of electrode 42 has a coating of fluorescentmaterial, to show where the beam strikes it; but when the adjustment iscompleted, such a coating will be of no particular use, since the beamwill notcome in contact with it.

Next, raise the potentials of the electrodes in zone E to about thevalues at which they should operate, and connect the load to thearmature. Then adjust the potentials more accurately. If the potentialof electrode 44 is too low, the beam current'will flow to electrodes 42and 43 instead,

but normallythe current to 42 and 43 should be almost negligible. If thepotential of electrode 44 is too high, the electrons will strike it withmore force than necessary, and waste energy. This condition may bedetected by measuring the currents of electrodes 44 and 45; due tosecondary emission, the net current of electrode 44 will decrease, andthat of electrode 45 will increase, when their potentials are too high.The sum of the electrode currents in zone E will, of course, equal thebeam current.

When all the adjustments are properly made, the cathode-ray converterwill operate to convert D. C. power to A. C., with an efiiciency of 90to 95 per cent. This is better than the average 60 cycle rotaryconverter, and surpasses the efficiency of any device previously knownfor the generation of radio frequency power.

For radio telegraphy, the output can be controlled by switching the beamon and off. Various methods have been devised for controlling thecurrent according to the position of the telegraph key, for other typesof amplifiers, and the same well known methods can be applied here.

For telephony, or television, amplitude modulation can be accomplishedby modulating the beam current, This may be done by means of a controlelectrode, such as is used in a television picture tube, or by meansexternal to the cathode-ray tube.

If the low frequency signal is used to control only the beam current,while the electrode potentials are kept constant, the efficiency of theconverter will be reduced by 25 to 50 per cent, depending upon thedegree of modulation employed.

If, on the other hand, the potentials of electrodes in zone E are variedsimultaneously by an amount proportional to the variation of thecurrent, the efficiency of the converter may remain at the same highfigure (over 90 per cent) even when modulation is employed. In thelatter case, however, there may be more power lost in the D, C. circuitsoutside the tube, and particularly in the apparatus used to control thepotentials.

The modulation of output amplitude could be accomplished by modulatingthe amplitude of the A. C. supplied to the deflection system, or bymodulating the magnification factor of the deflection booster.

The output of the armature varies with the radial displacement of thebeam, and therefore depends on the deflecting force and the deflectionsensitivity. To allow the beam passage, electrode 42 would have to bebuilt like a sieve or a spiderweb, and some modification of electrodes44 and 45 would also be advisable. Even after such tials of zone E neednot change.

- some frequency, say f1.

changes in design, the efficiency with this method of modulation wouldbe lower than with the method mentioned first, but the less efficientmethod might be more convenient in some cases.

If frequency modulation is employed, there is no variation ofefficiency, since the output power remains fixed, The beam current andthe poten- Any of the known methods of frequency modulation may beapplied to the source supplying A. C. to the deflection zone B.Theoretically, the variation of frequency would cause a correspondingvariation in the radial displacement of the beam, unless the magneticfield of zone B or the potential of electrode 31 in zone C were variedsimultaneously. However, for the frequency deviation commonly used infrequency-modulation transmitters, the effect of frequency on deflectionsensitivity is too small to need such compensation.

There is one case in which it would be important to modulate thepotential of electrode 31, in order to modulate the magnification of thedeflection booster; when the converter is used as a modulatedoscillator. The deflection voltage, being derived from an armature whoseoutput voltage varies with the beam current, will likewise vary; and tokeep the beam at the normal radial displacement in zone D, themagnification of the defiection booster (zone C) must vary inverselywith the amplitude of the deflection voltage, Both beam current and thepotential of electrode 31 can be controlled by the same signal, throughsuitable auxiliary apparatus.

In any of the applications possible for my invention, the outputfrequency may be the same as the deflection frequency; but it mayequally well be some multiple of the deflection frequency, if thearmature is so designed. The structural difference between armaturesdesigned to operate at various multiples of the fundamental frequency issimilar to the difference between armatures designed for dynamos withvarious numbers of pairs of poles. Each armature may receive power fromthe beam, or deliver power to the beam, according to the nature of theexternal circuit to which it is connected, It does not matter whetherthe various armatures operate at the same or different harmonics of thedeflection frequency. If the net transfer of power is from beam toarmatures, a corresponding amount of power must be supplied by the'D. C.circuits of the beam, If the beam receives more power than it delivers,the potential of the collecting electrode in zone E can be reduced belowthat of the cathode 1; and the beam will persist in spite of thisopposition. It will then deliver D. C. power to the external circuit.

The converter can be used as a mixer, such as the first detector of asuperheterodyne. If desired, it can function as oscillator, or frequencymultiplier, or both, to produce one of the voltages mixed, withoutimpairing its operation as mixer.

The other functions have been explained above. The mixing functionoperates as follows:

The beam induces in the armature voltages of An external sourceconproduces currents of an- These currents induce a with componentswhose nected to the armature other frequency, say f2. voltage along thebeam, frequencies are the sum or difference of various multiples of f1and f2. By appropriate choice of armature design and beam velocity, mostof the undesired results of the mixing can be eliminated, leaving thefirst difference frequency (fl-f2, or fz-f1) as the only importantcomponent. This voltage modulates the velocity of the beam, cause vng. acorresponding variation in-the impact of ;he electrons strikingelectrode 44; secondary emission from electrode 44 then convertsthevelocitymodulation into an alternating current of the same frequency,flowing between electrodes 44 and 45. This A. C. is superimposed on theD. C. normally flowing to said electrodes.

If f1 equals f2, the difference frequency will be zero. The inducedvoltage along the beam will then be A. C. at zero frequency, which issynonymous with D. C.

The operation as a mixer can be improved by using the output voltage(due to the A. C. flowing in a suitable impedance in the circuitconnecting electrodes 44 and 45) to adjust the instantaneous potentialsof electrodes 42 and 43, in order to keep the beam velocity nearlyconstant in zone D. This adjustment does not affeet the impact of theelectrons on electrode 44, which is determined by the relation betweenthe potential of electrode 64 and the voltage induced along the beam.Only a little power is required to control the potentials of theelectrodes 42 and 43, since very little current flows to them.

Although I have referred to the space discharge mostly as a beam ofelectrons or a cathode-ray, this is not a necessary limitation. Protons,deutrons, positrons, or any other charged particles could be used in aspace discharge, and would serve my purpose; but at the present state ofthe art, electrons are more readly available. If positively chargedparticles were used, the polarity of inter-electrode voltages would bethe opposite of that used with electrons.

I have shown a case in which the discharge passes lengthwise through thedischarg chamber, and in which a portion of the discharge path rotatesperiodically. This form is probably the most convenient, but in otherembodiments of my invention the discharge might follow a morecomplicated path, and it might have reciprocating instead of rotarydeflection.

For example, the discharge path might be a spiral, or a circular are, asin the Lawrence cyclotron; nevertheless, if one or more conductors canbe placed near a portion of that path, and approximately parallel to it,any deflection applied to the discharge before it passes the conductorswill shift the path and vary its distance from them; and this variationwill generate voltage in the conductors by electromagnetic induction.

While I have shown a particular form of embodiment of my invention, I amaware that many minor changes therein will readily suggest themselves toothers skilled in the art without departing from the spirit and scope ofthe invention; what I claim as new and desire to protect by Let tersPatent is:

l. A cathode-ray tube, an electron gun disposed within the tube fordischarging and directing a beam of electrons, means for deflecting thebeam, means for magnifying the displacement resulting from thedeflection and neutralizing the effect of the deflection on thedirection of the beam path, an armature wherein alternating voltages maybe induced by periodic displacement of the beam due to deflection at acorresponding frequency, and a plurality of electrodes for collectingthe electrons at the end of their passage through the tube.

2. A cathode-ray tube, an electron gu disposed within. the tube fordischarging and directing a beam of electrons, a plurality of electrodesfor collecting the electrons at the end of their passage through thetube, means interposed between. the electron gun and the electrodes fordeflecting the electronsin arotary fashion and for boosting thedeflection of the electrons in their passag from the gun to saidelectrodes, said deflecting means comprising-a plurality ofdiametrically opposed. deflection plates, said booster comprising aplurality of electrodes having central apertures of progressivelyincreasing diameter, and an armature comprising a plurality ofconductors adjacent to, the tube disposed generally parallel to thebeam, and interconnected at their extremities, wherein alternatingvoltages may be induced by periodic displacement of the beam due to.deflection at a corresponding frequency.

3. A method of converting power from direct current to alternatingcurrent, comprising the steps of discharging electrons in a beam,periodically displacing thepath of the beam transversely in asubstantially circular patternto produce a periodic variation in thedistances between the beam and adjacent conductors disposed generally inthe direction of the beam to induce alternating voltages in theconductors, allowingsaid voltages to cause alternating currents in' theconductors, then collecting the electrons at the end of their travel.

4. A-method of converting power from direct current to alternatingcurrent, comprising the steps of discharging electrically chargedparticles in a beam, periodically displacing the path of the beamtransversely in a pattern forming a closed curve to produce aperiodicvariation in the distances between the beam and adjacent conductorsdisposed generally in the direction of the beam to induce alternatingvoltages in the conductors, allowing said voltage to cause alternatingcurrents in-the conductors, then collecting'the particles at-the end oftheir travel.

5. A device for producing a beam of electrically charged particles,comprising a source of electrically charged particles, a group ofelectrodes near this source to produce anelectrostatic field, one of'saidelectrodes having an eperture to provide egress for theparticles,and a magnetic field disposedperpendicular to the electrostatic field,said magnetic field extending throughout the major part of the region inwhich the electrostatic fleld acts upon the particles.

6. A method of'generating alternating voltages comprising the steps ofproducing a space discharge, and controlling the path ofthe discharge insuch fashion as totrace out a closed curve to cause a periodic variationin" the distance between the discharge and adjacent conducting meansdisposed generally in the direction of the discharge, thereby inducingalternating voltage in the conducting means;

"I; A method of generating voltage in series with a space discharge,comprising the following steps: producing a'space discharge in suchfashion as to traceout a closed curve, controlling the path ofthedischarge to cause a periodic variation in the distance between-saiddischarge and adjacent conducting means: disposedgenerally in thedirection of the discharge, and causing to flow in the conducting meansalternating current whosefrequency differs from the frequency of thedesired voltage by the frequency of the voltage which the dischargeinduces in the conducting means.

8. A cathode-ray tube, an electron gun disposed within the tube fordischarging and directing a beam of electrons, a plurality of electrodesfor collecting th electrons at the end of their passage through thetube, means interposed between the electron gun and the electrodes fordeflecting the electrons in such fashion as to trace out a closed curvedand for boosting the deflection of the electrons in their passage fromthe gun to said electrodes, said deflecting means comprising a pluralityof diametrically opposed plates having terminal connections forsupplying the plates with fluctuating potentials for beam deflectionpurposes, and said booster comprising a plurality of electrodes havingcentral apertures of progressively increasing diameter, and havingterminal connections for maintaining them at desirable potentials, andan armature comprising a plurality of conductors adjacent to the tubedisposed generally in the direction of the beam, wherein alternatingvoltages may be induced by a periodic displacement of the beam due todeflection at a corresponding frequency.

9. A device for reducing the cross-sectional area of a beam ofelectrically charged particles, comprising means for producing anelectrostatic field, means for producing a magnetic field disposedperpendicular to the electrostatic field, said means for producing anelectrostatic field being provided with apertures to allow the beam toenter the field in one direction substantially perpendicular to themagnetic field, and to leave in another such direction substantiallyperpendicular to the first, and said magnetic field extending throughoutthe major part of the region traversed by the particles between theapertures.

10. In a space discharge device requiring a periodic deflection of thedischarge, a method of counteracting the adverse effect of transit timeupon deflection sensitivity, and of producing a circular or ellipticaldeflection only slightly affected by the deflection frequency, whichmethod is as follows: producing at least one transverse field in aregion traversed by the discharge, whereby the particles composing saiddischarge are accelerated transversely in the direction of the forceexerted on them by the transverse field; producing within the sameregion a longitudinal magnetic field substantially parallel to the average direction of the discharge within that region whereby thedischarge is further deflected, the particles being acceleratedtransversely at right angles to their transverse velocity, so that thedirection of their transverse velocity is gradually rotated; varyingsaid transverse field at the frequency desired for deflection of thedischarge; and adjusting the intensity of said longitudinal magneticfield to substantially the critical value at which the gyromagneticfrequency is equal to the frequency of variation of the transversefield, by which adjustment the rotation of the transverse velocity ofthe particles is made synchronous with the alternations of thetransverse field, and successive half-cycles of the transverse field aremade additive in respect to the total transverse momentum of theparticles, even though opposite in direction, and the transversemomentum of the particles increases continually as they progress throughthe region under the joint influence of the aforementioned fields.

11. In a space discharge device of the cathode ray type, means fordeflecting the beam of charged particles comprising the following: aplurality of electrodes adjacent to the path of the beam means forvarying the potentials of the electrode; at a high frequency, to producetransverse elec' trostatic forces acting on the discharge; a pluralityof permanent magnets disposed generall: parallel to the path of thebeam; annular pol pieces of magnetic material at the ends of thtpermanent magnets, to direct the magnetic fielc axially through theregion between the aforesaid electrodes; coil means coaxial with thepole pieces; means for producing a direct curreni through the coilmeans, and means for adjusting the intensity of the current, to adjustthe intensity of the magnetic field within the discharge chamber.

12. A cathode-ray tube, an electron gun disposed within the tube fordischarging and directing a beam of electrons, a plurality of electrodesfor collecting the electrons at the end of their passage through thetube, means interposed between the electron gun and the electrodes fordeflecting the electrons in such fashion as to trace a closed curve onthe collecting electrod and boosting the deflection of the electrons intheir passage from the gun to said electrodes, said deflecting meanscomprising a plurality of diametrically opposed deflection platestogether with means for producing a magnetic field along the beam, saidbooster comprising a plurality of electrodes having central apertures ofprogressively increasing diameter, and an armature comprising aplurality of conductors adjacent to the tube wherein alternatingvoltages may be induced by periodic displacement of the beam due todeflection the main conductors of said armature being disposed generallyparallel to the beam in such manner that the distance from the beam tothe nearest conductor will be substantially uniform throughout thelength of the armature.

13. In a space discharge device employing a beam periodically displacedtransversely in a rotary fashion and inductively coupled to adjacentconducting means, the arrangement of said conducting means comprising aplurality of longitudinal conductors disposed generally in the directionof the beam and interconnected at their extremities to form an armature,characterized in that the longitudinal conductors are skewed withrespect to the axis of rotation of the beam by substantially the amountnecessary to make the distance from the beam to the nearest conductoruniform throughout the length of that conductor.

14. An armature as in the preceding claim, characterized in that thelongitudinal conductors are skewed with respect to the axis of rotationof the beam by an amount substantially equal, on the average, to thatskew which would make the distance from the beam to the nearestconductor uniform throughout the length of that conductor, and furthercharacterized in that the maximum and minimum skew of the conductorsdiffer from the average by substantially the amount which would berequired for that average according to the relation stated above, if thebeam traveled with the velocity of electromagnetic waves.

ROBERT E. McCOY.

